In the last years the application of an artificial heart has become a clinical practice. Most of the blood pumps which are implanted into the body are driven by air, the pressurized air is delivered by a driving system located outside of the body. The pneumatic tubes leading to the blood pumps penetrate the skin and often lead to infections. Moreover, the driving systems are clumsy and limit the activity of the patient. These disadvantages pose severe limitations to the therapeutic value of such a pneumatic artificial heart or cardiac assist system. A possible solution to these problems is a totally implantable system. The energy can be transmitted into the body according to the transformer principle, one coil being implanted under the skin of the patient, the other being energized by a battery and placed close to the skin outside the body. The electric energy brought into the body in this manner then has to be converted into mechanical energy. A brushless electric motor is one of the proven ways to perform this task. However, the rotary energy of the motor has to be converted into a displacement of the walls of the blood pump, usually made of a flexible and blood compatible material. Mechanical systems have been designed which make use of a cam or a rollerscrew. It has been shown that these systems can work safely over an extended period of time, but still there is a general agreement, that minimizing the number of movable parts improves the inherent safety of such an energy converter. Attempts to move in this direction have been made with electrohydraulic systems. One system utilizes an axial flow pump, which consists of an impeller directly attached to the rotor of an electric motor. The impeller moves a transmitter fluid, the latter acting on the diaphragms of the blood pumps. The blood pumps require an alternating flow of the transmitter fluid, which is achieved by means of reversing the motor of the axial flow pump. This device has only one moving part and should have a great potential for safety. In practice, however, the simplicity is lost because the reversing action of the motor forbids the use of hydrodynamic bearings and requires ball bearings. Thus, in fact, more parts are introduced and those ball bearings pose a problem because of their limited durability. Another electrohydraulic energy converter makes use of a continuously running radial flow centrifugal pump. The alternating flow required by the blood pumps is generated with the help of a sleeve valve. So another element was introduced.
It is apparent to one skilled in the science of engineering that the prior art in the field has not successfully solved the problem of the energy conversion. The systems that have become known or partially have been applied in the clinical practice have severe disadvantages, mainly that the safety is not optimal. Obviously, if only one moving part could perform the desired task, the inherent safety would be greater than in the systems presently known. Safety of the system finally is the most important quality for the patient, who is physically and, as a human being, psychologically depending on the proper and safe functioning of the system.